The present invention, which has been developed with the participation of "Manufacture Francaise des Pneumatiques MICHELIN" concerns the conversion of used or waste tires to liquid and gaseous fuels.
The conversion of used tires has become a major problem since the most common way to get rid of them is to throw them out or, in some cases, to burn them in open air, thus releasing substantial amounts of carbon and polluting gas in the atmosphere. Other applications have been considered but they are unable, separately or not, to consume the huge amount of waste tires. The problem is the more serious as the number of waste tires in the world continuously increases and presently reaches several hundred millions of units per year.
A known conversion technique is pyrolysis. It is effected at a particularly high temperature and its relative complexity requires use of production units of large capacity, hardly compatible with a limited supply by sector due to the high gathering and transportation costs.
Another known technique consists of cutting the tires into fragments of various sizes, of heating these fragments in a heavy oil at a temperature from about 300.degree. to 500.degree. C. and of recovering the resultant products. The tire cutting step alone corresponds to a substantial part of the cost of the operation, particularly when effected on tires with metallic casings or on large size tires.
The treatment of whole tires by an immersion technique would require the use of a high quantity of oil, amounting to about 8 to 10 times the weight of the tires. The use of such an amount of oil results in serious disadvantages: delays in starting the installation and power consumption for heating the oil up to the reaction temperature, particularly in batchwise operated installations which are less adapted to heat recovery than continuously operated units.
Another difficulty arises from the foam formation in the apparatus where the tires are heated, which necessitates proceeding slowly in order to avoid clogging the apparatus. However the length of the treatment time required at high temperature too largely favours cracking and formation of gas to the detriment of liquid fuel.